Silica-coated expanding agents and their use in cementitious systems

Abstract

The invention relates to a process for preparing silica-coated particles of an inorganic expanding agent, the silica-coated particles and their use. The silica-coated particles show a delayed release of the expanding agent particularly in alkaline medium and at elevated temperatures. They are therefore useful in the oil and construction industry.

Description

[0001]The invention relates to a process for preparing silica-coated particles of an inorganic expanding agent, the silica-coated particles and their use.BACKGROUND[0002]Cementitious systems harden with a slight loss in volume (shrinkage). As a consequence thereof, crack formation may occur which impairs the strength of the concrete. In the oil and gas industry bonding between set cement and casing or formation is reduced so that a small gap or microannulus may form at the cement / casing and / or cement / formation interface, in particular under the thermal and mechanical stress that occurs in connection with oil and gas drilling operations. Under these circumstances an effective zonal isolation cannot be achieved.[0003]To avoid the shrinkage expansive cements have been used which are hydraulic cements that, after setting, increase in volume to significantly greater degree than Portland cement paste to form an expanded set cement. The increase in volume is often achieved by adding expand...

AI Technical Summary

Benefits of technology

The patent text describes a process for making silica-coated particles of an inorganic expanding agent. These particles can be used in cementitious systems. The process involves contacting particles of the expanding agent with a solution or dispersion of silica precursor, converting the silica precursor to silica, drying the coated particles, and subjecting them to a heat treatment. The technical effect of this process is that it provides particles that have improved properties, such as increased solubility and reduced agglomeration, which makes them easier to use in cementitious systems.

Problems solved by technology

As a consequence thereof, crack formation may occur which impairs the strength of the concrete.

Under these circumstances an effective zonal isolation cannot be achieved.

However, the use of such expanding agents is problematic since the expanding agents known in the art begin to hydrate and thus begin to expand as soon as they contact water (CaO) or begin to hydrate too late as they are very slowly reacting (MgO).

Therefore, the expanding agent can in many cases not be added to the cement slurry because the expanding agent is going to expand too early, i.e. before the cement slurry is positioned at the desired location leading to significant disadvantages.

Coating of metal oxide particles with non-hydratable or previously hydrated minerals such as metal carbonates, hydroxides and hydrates was suggested in U.S. Pat. Nos. 4,332,619, 5,741,357, EP2169027A1; but these materials can be difficult to prepare and have had only limited success.

Such a product is unsuitable as an expanding agent for cement mainly due to the small particle size and the thin coating.

Due to the development of hydrogen and the instantaneous reaction with water the protected aluminum flakes are unsuitable as an expanding agent for cement.

The hardening accelerator is unsuitable as an expanding agent for cement.

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